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Say what you want to say about this picture -

it speaks for itself

A certain member claims that this tyre was purchased only about 3 years ago, and had only about 3,800 Km on it!!

I won't say what brand it was, but I understand that the story is true.

He (quite wisely) decided to abandon his journey.

The rider concerned always checked the tyres prior to each run (as we all do). But (he admits) the check consisted mostly of looking at the back and front wheels and checking that the tread looks ok. However, the check on the rear tyre did not go beyond this - if the front and what was visible of the back seemed ok, then it was assumed that the rest of the tyre was ok also, on the basis that the wheel would be in a different position each time it was checked, and the check was often enough. It was, in effect, a series of random checks.

I suppose, statistically speaking, for a large number of random observations with each observation yielding the same result (in this case, tyre ok), it may be fair to say that the chance that a successive observation will yield a different result (tyre not ok) is low. This may be one of the assumptions behind quality control, but in the real world it has no real validity and is surely not to be trusted where your safety is concerned.

It's like this: imagine that at 3 am one morning you made an observation every minute for half an hour (a sample of 30 observations, a valid small-statistics sample size). In the whole half hour only six cars passed; this makes for only one car every five minutes. Would you then cross the highway with your eyes closed immediately after the last car you observed has passed, on the assumption that there is a low probability that there would be another car before the next five minutes?

Maybe it's only one in a thousand chance that you may come to grief - a low probability - but would you take even that low probability chance??

You cannot trust statistics with your life.

So when you make your pre-run tyre check, roll the bike along so that you can observe the whole tyre, all the way around.

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